Twitter used to do the same thing in reply tweets. Since mastodon basically just does what twitter did, they decided to clone that feature too. On mastodon, Lemmy posts just look like really long tweets a lot of the time, but with the magic of federation they can reply here too.
It is quite annoying when it gets deep and comments begin with 20 different @'s, but itâs just something mastodon does and I donât think they can control it
StudChud@aussie.zone âš5â© âšmonthsâ© ago
Itâs because you can access Lemmy from other fediverse sites, like Mastodon. Iirc, Mastodon is like Twitter, so when replying to a thread or comment, the reply will @ the users they are responding to